1. Field of the Invention
The present invention relates generally to a fuel supply system for an internal combustion engine of a vehicle and, more particularly, to a fuel supply system for regulating the quantity of fuel supplied to a fuel injector in a direct injection internal combustion engine to which fuel must be supplied at a high pressure.
2. Description of the Background Art
Conventionally, an electronically controlled fuel supply system used in an internal combustion engine of a motor vehicle includes a plurality of fuel injectors for injecting fuel into individual cylinders of the engine, a delivery pipe for feeding the fuel to the fuel injectors, a high-pressure fuel pump for feeding the pressurized fuel to the delivery pipe, a low-pressure fuel pump for feeding the fuel from a fuel tank to the high-pressure fuel pump, and a controller for controlling such parameters as fuel injection timing and injection quantity as well as discharge rate of the high-pressure fuel pump.
The aforementioned high-pressure fuel pump includes a cylinder, a pump piston and a solenoid valve. Controlled by a pump actuating cam fitted on a rotary shaft of the internal combustion engine, such as a camshaft, the pump piston reciprocates inside the cylinder, whereby the high-pressure fuel pump draws the fuel into a pressure chamber formed between the cylinder and the pump piston in each successive intake stroke and delivers the pressurized fuel from the pressure chamber to the delivery pipe in each successive output stroke. In the high-pressure fuel pump thus structured, the solenoid valve relieves the pressure of the pressurized fuel in the pressure chamber to a low-pressure side with specific timing to thereby regulate the quantity of fuel discharged from the pressure chamber, so that the fuel in the delivery pipe is maintained at a specific pressure level.
The fuel in the delivery pipe is normally held at the specific pressure level as the solenoid valve regulates the rate of fuel discharge from the pressure chamber as mentioned above. If it becomes impossible to properly regulate fuel pressure in the delivery pipe, however, the fuel injectors would not be able to inject the fuel in an optimal state and this makes it impossible to produce a mixture of a desired condition. Should such a situation occur, it is likely that combustion efficiency of the internal combustion engine drops, resulting in deterioration of running performance of the vehicle, or harmful emission gases are released from the engine. Thus, it is important that the solenoid valve properly regulate the quantity of fuel discharged from the pressure chamber all the time.
It is necessary to control the solenoid valve in such a manner that the solenoid valve opens and closes with proper timing according to the amount of lift of the pump actuating cam. Thus, in a prior art arrangement, a sensing signal of a crank angle sensor for detecting crank angle, or the angular position of a crankshaft, is used as a rotational position signal indicating the angular position of the pump actuating cam for controlling open/close timing of the solenoid valve.
If there is an error in mounting position of the high-pressure fuel pump or the pump actuating cam is mounted on other than the crankshaft, causing an error in angular position between the crankshaft and the pump actuating cam, however, the sensing signal output from the crank angle sensor would not indicate the correct angular position of the pump actuating cam. This would make it impossible to properly control the open/close timing of the solenoid valve.
A previous approach to the resolution of the aforementioned problem is found in Japanese Patent No. 2836282 which describes a fuel injection system provided with a delivery pipe, wherein an error in angular position between a crankshaft and a pump actuating cam is corrected based on a phase difference between a sensing signal output from a cam angle sensor mounted at the pump actuating cam and a sensing signal output from a crank angle sensor.
Another previous approach to the resolution of the aforementioned problem is found in Japanese Patent Application Publication No. 2003-41985. Although this Publication does not include a description with respect to the position of a pump actuating cam, a fuel injection system disclosed in the Publication has a capability to detect a delivered fuel quantity property corresponding to operating conditions from changes in fuel pressure occurring in response to a delivered fuel quantity command given at engine start.
The aforementioned fuel injection system of Japanese Patent No. 2836282 can correct the error in angular position occurring between the crankshaft and the pump actuating cam by using the detected phase difference between the sensing signal of the cam angle sensor and the sensing signal of the crank angle sensor. If there is an error in relative mounting position of a high-pressure fuel pump and the pump actuating cam, however, the fuel injection system of Japanese Patent No. 2836282 can not correct this error and this potentially causes an error in the quantity of fuel delivered by the high-pressure fuel pump. This is because the fuel injection system simply detects the phase difference between the sensing signals of the cam angle sensor and the crank angle sensor. If the fuel pressure in the delivery pipe can not be regulated to a specific level, fuel injectors would not be able to inject the fuel in an optimal state and produce a mixture of a desired condition. Should this situation occur, combustion efficiency of the internal combustion engine may drop, resulting in deterioration of vehicle running performance or of exhaust gas quality.
The fuel injection system disclosed in Japanese Patent Application Publication No. 2003-41985 detects the delivered fuel quantity property at engine start under conditions involving the influence of engine operating conditions, such as engine temperature, in addition to variations in individual system parameters. Although the fuel injection system of Japanese Patent Application Publication No. 2003-41985 can regulate the quantity of fuel delivered by the high-pressure fuel pump with high precision at engine start, the quantity of the actually delivered fuel varies with changes in engine operating conditions after engine start, such as an increase in engine temperature. Therefore, an error is likely to occur in the detected delivered fuel quantity property.